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Question Hi! We build medical equipment that use a number of PCBs (many EPROMS). How close can a person move their hand across or around the PCBs without a ESD wrist strap ? Thank you... - Anonymous, Riverside, CA,
Answer Typically, ESD Control programs do not allow ungrounded users to enter an ESD Protective Area (EPA). If a person needs to enter an EPA and is not grounded, then there is concern.

To answer your specific question, if we were to treat an ungrounded users as an process essential insulators, then when they have electrostatic fields that exceed 2,000 volts they should be kept at a minimum distance of 12 inches from Electrostatic Susceptible (ESDS) items. 2,000 volts is a measure of the electrostatic field at the point of measurement and is not necessarily directly related to the electrical potential of the item. Also realize that a person's capacitance can easily change (a decrease in capacitance from a reduction in surface area contact or proximity with ground can yield a much higher potential field [V/m] from the lumped circuit equation [V=Q/C]).
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